This invention concerns an improved structure of tank devices of the type horizontally installed and utilized in operating impregnation of heated and melted pitch therein. More particular the invention relates to an improved structure of the lid member and the sealing arrangement for such tank device.
Today a wide use is made of carbon electrodes for example in the electric furnace for steel making or in many other heating apparatus for various purposes, and with carbon electrodes used in electric furnaces in particular, instances are observed in which electrodes are so large in size as to have a diameter in the order of from 50 cm to 150 cm.
In the manufacture of such carbon electrodes, particles of a carbon material such as coke or the like blended with a binder material so as to impart a viscosity thereto are extruded to a rod like product and subjected to a high temperature application to there obtain a blank electrode. The blank electrode thus obtained, which is porous, has an only insufficient strength and cannot stand for use in an electric furnace, per se. Therefore, in order to manufacture a product electrode having desirable characteristics such as a sufficient rigidity and capacity for a large electric current density, it is known and practised to subject the blank electrodes to a pitch impregnation treatment, which generally is worked with use of a horizontally disposed tank device. Pitch impregnation tanks or pitching tanks under consideration normally comprises a cylindrical body portion and a lid member releasably secured to the open side end of the body or two lid members respectively disposed at each open end of the body if the latter is open at both ends.
In operation of the pitching treatment, as soon as blank electrodes are conveyed into the pitching tank, as received on a palette and heated in a hot air furnace at a temperature above the melting point of pitch, deaeration will be operated to there provide a vacuum condition within the tank, followed by charging into the tank of pitch melted and maintained at a high temperature. Whereas when the pitch impregnation is complete after the lapse of the prescribed length of time a predominant portion of the charge of pitch has become impregnated into blank electrodes, it usually occurs that a fair amount of pitch is permitted to still remain within the tank. Accordingly, in taking out the pitched blank electrodes from the tank, it is usually operated to first remove away the portion of pitch unused or unabsorbed in the electrode blanks and remaining present in the tank.
A difficulty is indicated in this connection that with the current tank apparatus hardly feasible is to completely remove away such an unused pitch portion as attached about the inside surface of the tank or about the surfaces of the pitched elecrode blanks. Unused surplus portions of pitch, amount of which is fairly great when all are collected together, tend to flow out of the tank upon opening of the lid and pollute the floor of the workroom.
Another difficulty indicated is that whereas upon opening of the tank the surplus or unused portion of pitch flows down gradually along the surfaces of flange portions formed of both the tank body and the lid, if said flange portions are not manintained at a sufficiently high temperature it occurs that the surplus pitch portion becomes gradually attached and hardened about the flange portions and the seal member such as an O-ring as well; if it occurs, not only the seal member is permitted to undergo a local deformation or other damages caused by the hardened portion of pitch but also made difficult is to have the tank satisfactorily shut by the lid for a next pitching operation cycle, and it inconveniently is unavoidable to conduct a manual cleaning operation of the tank at each time of the opening of the tank lid, for removing the pitch portion tending to attach and harden about flange surface portions.
A still another difficulty, which has derived from a recent tendency in this field of art to employ a higher temperature than before for heating pitch so as to enhance the pitch impregnation efficiency, resides in that cases are encountered oftener today than before in which the temperature of heated pitch exceeds the allowable temperature of the material for the seal member, whereby made more difficult today is to provied a satisfactory seal between the tank body and its closing lid.